Three-port circulator comprising only two crossing coils

ABSTRACT

Three-port circulator comprising only two windings crossing each other at right angles so that the number of stray capacitances as compared with existing circulators is reduced and the bandwidth is less restricted.

United States Patent [72] Inventor Hendrik Bosnia Emmasingel, Elndhoven,Netherlands [2|] Appl. No. 49,392 [22] Filed June 24, 1970 [45] PatentedNov. 16, 1971 [73] Assignee U. S. Phlllps Corporation New York, NY. [32]Priority July 2, 1969 3 3 Netherlands 3 l 1 69101 16 [54] THREE-PORTCIRCULATOR COMPRISING ONLY TWO CROSSING COILS 1 Claim, 3 Drawing Figs.

[52] U.S.Cl

[51] Int. Cl HOlp 1/32, H0 l p 5/ l 2 [50] FieldolSearch 333/l.l, 24.2

[56] References Cited UNITED STATES PATENTS 2,944,229 7/1960 De Vries333/242 3,5l9,957 7/l970 Omori 333/l.l

Primary Examiner Herman Karl Saalbach Axsisran! Examiner--Paul L.Gensler Attorney-F rank R. Trifari ABSTRACT: Three-port circulatorcomprising only two windings crossing each other at right angles so thatthe number of stray capacitances as compared with existing circulatorsis reduced and the bandwidth is less restricted.

PATENTEDuuv 16 19?: 3,621,477

INVIENTOR. HENDRIK BOSMA THREE-PORT CIRCULATOR COMPRISING ONLY TWOCROSSING COILS The invention relates to a three-port circulatorcomprising at least one disc-shaped, ferromagnetic body prepolarized bya static magnetic field at right angles to the parallel major surfacesand comprising two windings located in intersecting planes parallel tothe static magnetic field, said windings being coupled with theelectromagnetic field in the disc and being connected to each other atone end and to connecting terminals at the other end.

Such a nonreciprocal device is connected by the connecting terminals totransmission lines. For matching the impedances of the windings to thoseof the transmission lines reactive networks are provided, which provideon the one hand a real input impedance by tuning the inductances of thewindings at the working frequency and on the other hand adapt theseimpedances to the desired level in the frequency range of maximum width.When one of the transmission lines supplies energy to the circulator,this energy is passed totally, apart from losses in the circulator, tothe next-following transmission line, energy supplied by the latter tothe circulator is transmitted to the next-following transmission lineand the energy supplied by the latter to the circulator is again passedto the first transmission line.

Owing to this circulator property the known devices have a threefoldrotation-symmetrical structure. Such a circulator is known, for example,from German Pat. application (D.A.S.). 1,259,421; said circulatorcomprises three windings whose winding planes intersect each other atangles of 120. These windings cross each other approximately at thecenter of the disc. At the area of the crossings on either side of thedisc stray capacitances occur between the windings. This constructioncomprising three crossing windings has the disadvantage that the numberand the magnitude of these stray capacitances involve a restriction ofthe bandwidth of the circulator. The circulator according to theinvention mitigates this disadvantage because only one stray capacitanceoccurs, which can be readily kept at a low level because structuralpossibilities are less restricted.

The invention is characterized in that only two windings are provided,which cross each other at right angles approximately at the center ofthe disc, said windings being connected to each other at one end througha conductor along the edge of the disc, a third connecting terminalbeing provided approximately midway said conductor.

It would be noted that a nonreciprocal, electric coupling device havingtwo orthogonally crossing windings is known, which windings are coupledby means of a magnetically prepolarised ferrite body, there being,however, a purely imaginary impedance coupled with the windings.Moreover, this device is driven at the ferromagnetic resonance of theferrite. The purpose is to utilize the resonance of the electron spinsin the ferrite and no use is made of circuit resonance (resonance of thereactive network with the inductance of the winding). This devicerequires energy dissipation in the ferrite. Moreover, it comprises onlyone input terminal and one output terminal, so that it does notconstitute a circulator but a unidirectional insulator.

The invention will be described more fully with reference to theembodiments shown in the FIGS., corresponding parts of the FIGS. aredesignated by the same references.

F 16. 1 shows schematically a known circulator.

FIGS. 2 and 3 show circulators according to the invention in a schematicview.

The known circulator shown in FIG. 1 comprises a discshaped,ferromagnetic body 4, which is prepolarised by a static magnetic fieldH. The connecting terminals 1,2 and 3 are connected for example, viacapacitor C to the windings W,, W and W which are represented in theF16. bythreequarter turns. These windings intersect each other at anglesof 120", are interconnected at point p and cross each otherapproximately at the center of the disc. The stray capacitance betweenthe windings W, and W is designated by C that between W, and W by C andthat between W and W by C13.

lt is supposed that the winding W is located between the windings W, andW so that: C =C --2C-. Because three windings are provided, three straycapacitances occur, the values of which are, moreover, difierent. Owingto the highly restricted structural possibilities because of thenecessity of an optimum magnetic coupling of the windings in order toavoid leakage fluxes, it is difiicult to minimize these capacitances.The bandwidth of the circulator is strongly restricted by thesecapacitances. v

The circulator shown in FIG. 2 in accordance with the inventioncomprises two windings w, and W each formed by half a turn crossing eachother at right angles approximately at the center of the disc andconnected at one end through capacitors C to the connecting terminals 1and 2 and at the other end to a conductor G, which follows the edge ofthe ferrite disc. A third connecting terminal 3 is providedapproximately midway the conductor G. From the FIG. it will be apparentthat only one stray capacitance 0,, can occur between the windings. Itcan, in addition, be readily minimized because there are only twowindings.

It may be provided by the law of energy continuity that a loss-free,nonreciprocal, matched tripole is a circulator (see, for example, H. J.Carlin, Polytechn. Inst. Brooklyn, Microwave Research Inst. SymposiaSeries Vol. 4, page 191, 1954). On this basis the operation of thecirculator may be accounted for as follows:

The relationship between the magnetic inductance and the magnetic fieldintensity in directions at right angles to the direction of magneticprepolarization of the disc is given by:

In the construction according to the invention two orthogonal windingsare used, which are coupled via the ferrite body. The mutual inductanceis thus determined solely by those proportionality factors whichindicate the relation between the magnetic inductance in one directionand the magnetic field strength in the direction at right anglesthereto. It will be apparent that the factor determining the relationbetween one winding and the other has an opposite sign to thatdetermining the relation between the other winding and the first winding(which qualifies the nonreciprocal behavior) and that these factorsdiffers a factor j= *1 from those of any reciprocal mutual inductances.This means that the induced voltages are in phase or in phase oppositionto the voltage applied through the windings.

For matching the device to real transmission lines capacitors are usedthe value of which is such that at the working frequency the seriescombination of a capacitor and the inductance is obtained. Instead ofusing a single series-connected capacitor more complicated circuits ofreactive network elements may be employed for having the device matchingthe transmission lines in a wide frequency range. In correct operationthe connecting terminals are closed by a real resistance value, forexample, the characteristic impedance of the coaxial cable. The value ofthis resistance and the magnitude of the nonreciprocal mutual coupling,determined by the number of turns of each winding, the nature of theferrite, the strength of the prepolarized magnetic field and the workfrequency, are chosen to be equal.

The operation will be further explained with reference to FIG. 2.

When connecting a voltage source to terminal I and when using thecorrect resistance value for closing the connecting terminal 3 and anarbitrary value for closing terminal 2, the voltage induced by a currentthrough winding 1 in the winding 2 the static magnetic field having thedirection shown, will be equal to and in phase opposition to the voltageacross the resistor connected to terminal 3 so that the voltage atterminal 2 is zero. All energy then passes from connecting terminal 1 toconnecting terminal 3.

When the voltage source is connected to terminal 3 and when the terminal2 is correctly closed and the terminal 1 is closed arbitrarily, thecurrent through the winding 2 induces in winding 1 a voltage equal andin phase opposition to the voltage of the source. Terminal 1 is thenisolated and the energy passes from the connecting tenninal 3 toterminal 2.

When the voltage source is connected to terminal 2 and when the terminal1 is correctly closed and the terminal 3 is closed arbitrarily, thevoltage induced in winding 2 by the current through the winding 1 is inphase opposition to the voltage source connected to said terminal sothat the voltage at terminal 3 becomes zero, whereas the current throughwinding 2 induces in winding 1 a voltage producing a terminal volt ageat terminal 1, so that the energy passes from 2 to 1. By inverting thedirection of the static magnetic field, the direction of circulation isinverted.

In order to obtain an optimum value of the nonreciprocal coupling, thework frequency is chosen to be offset with respect to the ferromagneticspin resonance. It is thus ensured at the same time that the passattenuation can be kept low.

FlG. 3 shows a circulator according to the invention in a schematicview; the number of turns is an even-numbered multiple of half turns perwinding. This has the advantage that the three connecting terminals arelocated on one side of the disc.

What is claimed is:

l. A three-port circulator comprising at least one discshaped,ferromagnetic body prepolarized at right angles to the parallel majorfaces by a static magnetic field and comprising two windings located inintersecting planes parallel to the static magnetic field and coupledwith the electromagnetic field in the disc and connected to each otherat one via a conductor following the edge of the disc end and coupled atthe other end to connecting terminals said windings crossing each otherat right angles approximately at the center of the disc, a thirdconnecting terminal being provided approximately midway of saidconductor.

1. A three-port circulator comprising at least one disc-shaped,ferromagnetic body prepolarized at right angles to the parallel majorfaces by a static magnetic field and comprising two windings located inintersecting planes parallel to the static magnetic field and coupledwith the electromagnetic field in the disc and connected to each otherat one via a conductor following the edge of the disc end and coupled atthe other end to connecting terminals said windings crossing each otherat right angles approximately at the center of the disc, a thirdconnecting terminal being provided approximately midway of saidconductor.